Electromagnetic switching means



Feb. 28, 1956 H. w. LORD 2,736,841

ELECTROMAGNETIC SWITCHING MEANS Filed Aug. 24, 1951 His Attorney.

United States Patent() ELECTROMAGNETIC SWITCHING MEANS Harold W. Lord,Schenectady, N. Y., assignor to General Electric Company, a corporationof New York Application August 24, 1951, Serial No. 243,486

6 Claims. (Cl. 315-174) My invention relates to frequency selectiveelectromagnetic switching systems, and more particularly to carriercurrent switching systems especially adapted to control electricdischarge lamps and the like.

When discharge lamps, such as fluorescent lamps or the like, areconnected in multiple, or parallel, circuit relation for street lightingapplications, it may be desirable to control the energization andde-energization of the lamps remotely, as by a carrier currentelectromagnetic switching system.

It has been common practice to connect electric discharge lamps inparallel circuit relation to a pair of supply conductors throughseparate ballast-type autotransformers each having one extendedsecondary winding loosely coupled to the primary winding to provide aballast impedance for the connected lamp, and a second extendedsecondary winding closely coupled to the primary winding with a powerfactor correction capacitor connected across the closely coupledsecondary winding or across that secondary winding and a part or all ofthe primary winding. The power frequency is commonly 60 cycles persecond, and a commonly-utilized carrier frequency superimposed upon thesupply conductors has been 720 cycles per second. 4 l

With the foregoing arrangement, when it has been sought to control acarrier frequency responsive switching device or relay connected forenergization across the supply conductors, it has been found that thepower factor correction capacitor has provided such a low impedanceatthe carrier frequency that it virtually short-circuits the conductors,and thus so limits the voltage at carrier frequency that the relay hasfailed to operate.

- and improved carrier current switching system for electric dischargelamps and the like.

More specifically, it is an object of my invention to provide means forpreventing the power factor correction capacitor in a discharge lampballast transformer from effectively short circuiting the supplyconductors for voltages of carrier frequency.

In carrying out my invention in one form, I provide a lamp ballast ofthe auto-transformer type, wherein a primary winding is adapted to beconnected across the supply conductors through a carrier frequencyresponsive relay, a pair of oppositely extending secondary windings areconnected in series circuit relation with the primary winding atopposite ends thereof, and a power factor correction capacitor isconnected across the primary and one of the secondary windings, thedischarge lamp .load being connected across the primary winding and theother extended secondary winding. If desired, of course, the relaycontacts may be connected in the transformer output circuit. I soarrange the primary and secondary windings upon the ballast transformerthat a relatively large leakage inductance is provided between the pri-W 2,736,841 ce Patented Feb. 28, 1956 mary winding and the secondarywinding associated with the lamp, thereby to provide a ballastiimpedance for the lamp. Between the primary winding and the secondarywinding associated with the power factor correction capacitor, I providean appreciable but relatively small amount of leakage inductance, sothat for power frequency voltages the shunt path through the capacitoris effectively of capacitive reactance, while for carrier frequencyvoltages the small leakage inductance is such that the shunt paththrough the capacitor is effectively inductive in nature. This secondleakage inductance, the reactance of which is small at power frequencybut large at carrier frequency, thus acts as a series inductance in ythe capacitor circuit and serves to limit the current through v to suchauto transformers whether the power factor correction capacitor beconnected across only the associated secondary winding or across thatwinding in series with a part or all of the primary winding. Also, thetwo secondary windings may extend from the same end rather than fromopposite ends of the primary winding.

My invention itself will be more fully understood and its variousobjects and advantages further appreciated by referring now to thefollowing detailed specification, taken in conjunction with theaccompanying drawing, in which Fig. 1 is a schematic circuit diagram ofa frequency selective discharge lamp switching system embodying myinvention; and Fig. 2 is a diagrammatic cross-sectional representationof a lamp ballast transformer having the primary and various secondarywindings arranged thereon in accordance with my invention.

Referring now to the drawing, and more particularly to Fig. 1, I havethere shown an electric discharge lamp supply and switching systemcomprising a pair of supply conductors 1 having connected thereto inparallel circuit relation a source 2 of alternating electric currentsupply of power frequency, for example 60 cycles per second, and asource 3 of alternating electric current supply of an appreciably highercarrier frequency, for example 720 cycles per second. A pair of electricdischarge lamps 4 having terminals 4a and 4b are adapted to be energizedin parallel circuit relation from the power conductors 1, each throughan associated relay 5 having normally an open contact 5a and a tunedactuating winding 5b. The actuating windings 5b are connected forenergization across the supply conductors 1 and are selectivelyresponsive to the carrier frequency from the source 3.

For energizing the lamps 4 in parallel circuit relation, I provide foreach lamp a ballasting auto-transformer having a primary winding 6 and apair of opp'ositely extending secondary windings 7 and 8 connected inseries circuit relation with the primary winding. Each primary winding 6has a pair of input terminals 6a and 6b which are adapted to beconnected to the supply conductors 1 through the normally open contact5a of the associated relay 5. Each auto-transformer is of the iron coretype and is provided with a core 9, having the windings 6, 7 and 8mounted thereon. Both secondary windings 7 and 8 on each transformer areloosely coupled to the primary winding 6, insofar as an appreciableleakage reactance is provided between the primary winding and eachsecondary winding. As best shown at Fig. 2, this leakage reactance isprovided by magnetic shunts interposed between the windings, a shunt 9abeing interposed between the primary winding 6 and the secondary winding8 and a shunt 9b being interposed between the primary winding 6 and thesecondary winding 7. The core and the magnetic shunts are schematicallyindicated at Fig. 1 and are diagrammatically illustrated at Fig. 2,wherein the windings 6, 7 and 8 are shown in cross-sectional view. Itwill be noted from Fig. 2 that the magnetic shunt 9a between the primarywinding 6 and the secondary winding S, across which the lamp load isadapted to be connected, is of relatively large section, so that thesewindings are quite loosely coupled and the leakage reactancetherebetween is appreciable even at the low power frequency. On theother hand, the magnetic shunt 9b between the primary winding 6 and thesecondary winding 7 is of relatively small section, and the windings 6and 7, while loosely coupled insofar as some appreciable leakagereactance is intentionally provided therebetween, are more closelycoupled than are the windings 6 and 8. Thus, the leakage reactancebetween the windings 6 and 7 is of small, and indeed of relativelyinappreciable value, at the low power frequency, but is of appreciablevalue at the high carrier frequency.

Referring now more particularly to Fig. l, it will be observed that apower correction capacitor llt) is connected across the primary winding6 and the extended secondary winding 7 in series circuit relation. Aterminal 8a at the end of the secondary winding 3 and the terminal 6a ofthe primary winding constitute a pair of output terminals for thetransformer, across which the lamp 4 is connected. lt will of course beunderstood by those skilled in the art that in the general case the lampterminals 4a and 4b represent load terminals between which there may beconnected any desired type of electric load device, the electricdischarge lamps 4 being shown by way of illustration, since my inventionis particularly well adapted for use in conjunction with a load of thistype. It will be further understood that if desired the relay contacts5a may be connected between the load terminals and the transformeroutput terminals.

It will now be apparent that in operation, when the high carrierfrequency is applied to the power conductors l, the load relays 5 areenergized and close their contacts 5a, thereby to connect the dischargelamps 4 to the supply conductors through their respectiveauto-transformers. Upon such connection, the lamps 4 are energized fromthe power frequency source 2 through the transformer windings 6 and 8.As is well understood by those skilled in the art, the leakage reactancebetween windings 6 and 8 of each transformer, which is relatively largeat power frequency, serves as a series ballast impedance for theassociated discharge lamp 4. The leakage reactance between the windings6 and 7 is relatively low at power frequency, so that it has noappreciable effect upon the power factor corrective action of thecapacitor lt). For the high carrier frequency currents, however, theleakage reactance between the windings 6 and '7 is of high value, whilethe capacitive reactance of the capacitor l@ is lower for the highcarrier frequency currents than for the low frequency `power currents.By proper selction of constants, the leakage reactance between thewindings 6 and 7 is made less than the reactance of the capacitor itlfor power frequency currents and greater than the reactance of capacitor10 for carrier frequency currents, so that this leakage revactanceserves as a current limiting impedance in series with tht` capacitor 1t)for high carrier frequency currents, but has no appreciable effect uponthe power frequency currents.

While i have described a preferred embodiment of my :invention by way ofillustration, many modifications will loccur to those skilled in the artand I therefore wish to have it understood that l intend in the appendedclaims to cover all such modifications as fall within the true spiritand scope of my invention.

What I claim as new and desire to secure by Letters- Patent of theUnited States is:

li in a frequency selective electromagnetic switching system forenergizing an electric load device at the lower of two frequencies froma pair of supply conductors having connected thereto in parallel circuitrelation two sources of -alternating current supply of appreciablydifferent frequencies, an auto-transformer having loosely coupledprimary and secondary windings'providing a leakage reactance betweensaid windings which is relatively inappreciable at said lower sourcefrequency but which is appreciable at said higher source frequency, saidautotransformer having a pair of output terminals adapted to beconnected to said load device and said primary winding having a pair ofinput terminals adapted to be connected to said supply conductors, acapacitor connected across at least said secondary winding, and havingat said lower source frequency a reactance which is greater than saidleakage reactance and which at said higher source frequency is less thansaid leakage reactance so that said leakage reactance serves as acurrent limit impedance in series with said capacitor for said highersource frequency but has no appreciable effect upon current ow at saidlower source frequency and electromagnetic switching means connected toenergize said load device through said transformer, said switching meansbeing adapted to be connected for energization to said supply conductorsand being selectively responsive to the higher of said sourcefrequencies.

2. In a frequency selective electromagnetic switching system forenergizing an electric load device at the lower of two frequencies froma pair of supply vconductors having connected thereto in parallelcircuit relation two sources of alternating electric current supply ofappreciably different frequencies, an auto-transformer having a primarywinding and an extended secondary winding connected in series circuitrelation therewith and loosely magnetically coupled thereto, saidauto-transformer having a pair of output terminals adapted to beconnected to said load device and said primary winding having a pair ofinput terminals adapted to be connected to said supply conductors, acapacitor connected across at least said secondary winding, saidcapacitor having a capacitive reactance greater than the inductiveleakage reactance between said primary and secondary windings at thelower said frequency but less than said leakage reactance at the highersaid frequency, and electromagnetic switching means connected toenergize said load device through said transformer, said switching meansbeing adapted to be connected for energization to said supply conductorsand being selectively responsive to said higher frequency;

3. In a carrier current electromagnetic switching sysstem for energizingan electric load device at power frequency from a pair of supplyconductors having connected thereto in parallel circuit relation a lowfrequency source of power current supply and a high frequency source ofcarrier current supply, an auto-transformer having a primary winding andan extended secondary winding connected in series circuit relation,therewith, said auto-transformer having a pair of output terminalsadapted to be connected to said load device and said primary windinghaving a pair of input terminals adapted to be connected to said'supplyconductors, magnetic shunt means interposed between said primary andsecondary windings to provide a leakage reactance therebetween, acapacitor connected across at least said secondary winding, saidcapacitor having a capacitive reactance 'greater than said leakagereactance at said power frequency but less than said leakage reactanceat said carrier frequency, and electromagnetic switching meansconnecting said I input terminals to said supply conductors, saidswitchcoupled thereto, said primary winding having a pair of inputterminals adapted to be connected to the supply conductors, the leakagerea/.trance between one of said secondary windings and said primarywinding being appreciable even at the lower of said source frequencies,the leakage reactance between the other of said secondary windings andsaid primary winding being relatively inappreciable at the lower of saidsource frequencies but being appreciable at the higher of said sourcefrequencies, a capacitor connected across said primary winding and saidother of said secondary windings and having relative to the leakagereactance between said other secondary winding and said primary winding,a capacitive reactance which at said lower source frequency is greaterthan said last mentioned leakage reactance and renders its circuiteffectively of capacitive reactance and which at said higher sourcefrequency is less than said last mentioned leakage reactance and rendersits circuit effectively of inductive reactance limiting high frequencycurrent ow therethrough, a pair of output terminals on saidauto-transformer having connected therebetween said primary winding andsaid one of said secondary windings and adapted to be connected to theload device, and electromagnetic switching means connected to energizethe load device through said transformer, said switching means beingadapted to be connected for energization to said supply conductors andbeing selectively responsive to the higher of said source frequencies.

5. In a frequency selective electromagnetic switching system forenergizing an electric discharge load device at the lower of twofrequencies from a pair of supply conductors having connected thereto inparallel circuit relation two sources of alternating electric currentsupply of appreciably different frequencies, any auto-transformer havinga primary winding and a pair of oppositely extending secondary windingsconnected in series circuit relation therewith and loosely magneticallycoupled thereto, said primary winding having a pair of input terminalsadapted to be connected to said supply conductors, a capacitor connectedacross said primary Winding and one of said secondary winds, saidcapacitor having a capacitive reactance greater than the inductiveleakage reactance between said primary winding and said one secondarywinding at the lower said frequency but less than said leakage reactanceat the higher said frequency, a pair of output terminals on saidauto-transformer having connected therebetween said primary winding andthe other said secondary winding and adapted to be connected to saidload device, the leakage reactance between said primary winding and saidother secondary winding providing a load ballast impedance at said lowerfrequency,

and electromagnetic switching means connected to energize said loaddevice through said transformer, said switching means being selectivelyresponsive to said higher frequency and being connected for energizationto said input terminals.

6. lnr a carrier current electromagnetic switching system for energizingan electric discharge lamp load at power frequency from a pair of supplyconductors having connected thereto in parallel circuit relation a lowfrequency source of power current supply and a high frequency source ofcarrier current supply, an auto-transformer having a primary winding anda pair of oppositely extending secondary windings connected in seriescircuit relation therewith, said primary winding having a pair of inputterminals adapted to be connected to said supply conductors, magneticshunt means interposed between said primary winding and a first of saidsecondary Windings to provide therebetween a first inductive leakagereactance of low value at said power frequency, a capacitor connectedacross said primary and first secondary windings, said capacitor havinga capacitive reactance greater than said first leakage reactance at saidpower frequency but less than said lirst leakage reactance at saidcarrier frequency, magnetic shunt means interposed between said primarywinding and the other of said secondary windings to provide therebetweena second inductive leakage reactance of higher value than said firstinductive leakage reactance at said power frequency, a pair of outputterminals having connected therebetween said primary and said othersecondary winding and adapted to be connected to said discharge lamp,and electromagnetic switching means connecting said input terminals tosaid supply conductors, said switching means being selectivelyresponsive to said carrier frequency and being adapted to be connectedfor energization to said input terminals, whereby said second leakagereactance ballasts said lamp and said iirst leakage reactance limitscapacitor current upon carrier frequency application.

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